DIAGNOSING HOSTA PROBLEMS Janna Beckerman

Prevention:
In their natural environment, hostas thrive in part to full shade. Most varieties will thrive with just a few hours of morning sunlight.  Many thick leaved cultivars can tolerate part- to full sun with adequate water. Blue varieties develop better color if grown in open shade, with no direct sun.  Green and gold varieties, as a rule, will tolerate more sun provided they receive adequate amounts of water.  Hostas are hardy in zones 3 through 9.  The plants tend to grow larger and produce more intense, bluer and greener coloration in cooler climates. As a rule, hostas suffer fewer problems in areas with shorter growing seasons.

When planting hosta, prepare the planting site. Dig a hole deep enough to cover and not compact the roots. Position the crown at slightly above the soil line. Hostas thrive in moist, well draining soil. Depending on the variety and the density of the foliage you desire adequately space the plants 2 to 4 feet apart. Mature clumps of larger varieties (e.g., ‘Sum and Substance,’ ‘Blue Angel,’ ‘Great Expectation’ to name but a few!) may need even more space, miniatures may require less. Although many people prefer clumps of overlapping hosta and view these plantings as more aesthetically pleasing, the humid canopy encourages the spread of any developing crown rots. Additionally, leaf-to-leaf contact between plants facilitates the spread of disease, especially foliar nematodes.

Although low maintenance, hostas do require regular watering, especially when planted close to foundations, and during hot, dry periods of summer. When watering, minimize water on foliage, which spreads most diseases. Mulch to prevent the soil from drying out, and to keep roots cool. Leaves are prone to burn without adequate moisture, especially when planted in too much sun. Certain cultivars, like ‘Frances Williams,’ may burn even with this added care.

Diagnosing Hosta Problems- Cheat Sheet:

This key is meant as an aid, not a comprehensive treatise on diagnosing hosta problems. When in doubt, contact your local Extension office.

Leaves and Crown:

Symptoms	Possible Causes
Holes, notched or cut-leaves	Insects and molluscs. In warmer climates, black vine weevils commonly feed on edges. Other possible problems include cutworms and leaf-cutter bees.
Spots-tan to Brown-random	Fungal leaf spot. Remove severely infected leaves, minimize wet foliage
Spots, brown and clustered	Four-lined plant bug
Ringspots Mottling Deformity	Virus. Laboratory identification is needed to determine which type of virus, and needed management strategy.
Change in color	Sport virus
Blights Anthracnose	Leaf spots that expand down leaf veins and infect petioles. Use a handlens identify black fruiting bodies in lesion to confirm diagnosis.
Dead areas between veins	Foliar nematodes.
Scorch	Insufficient water Too much sun ‘Frances Williams’
Reduced Size	Inadequate water or fertilizer "weak cultivar" root rot
Reduced Number	Inadequate water or fertilizer "weak cultivar" root rot
Collapse	Hosta collapse after a few hard freezes in the fall. Burrowing animal damage. Check roots. Crown rot. Check for mycelial growth and "mustard seed-like" structures.

Roots:

Symptoms	Possible Causes
Brown	Root rot. Laboratory diagnosis to determine which one is essential to management.
Stubby Lesions	Nematode
Galls	Nematode

P153H
May 2004

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